Liquid cleaning system including back-flushing filter and centrifugal cleaner therefor

ABSTRACT

A liquid cleaning system, which includes a barrier type filter having a back-flush arrangement for recovering filter contaminants from the back-flushed liquid which is available only at a low, not necessarily consistent, rate, includes a fluid-powered centrifugal cleaner which, in addition to the normal shaft-mounted rotor through which liquid is passed to separate contaminants centrifugally due to rotor speed, includes fluid drive means in the form of fluid reaction drive nozzles supplied with pumped liquid from the system as a drive fluid to rotate the rotor at a speed above the minimum to effect centrifugal separation of the contaminants from the back-flushed liquid in the rotor and accumulation of the outlet of the rotor. The spent drive fluid mixes with the cleaned back-flushed liquid in a discharge region and both may be re-used in the system. The intermittently available cleaned liquid may emerge from the rotor by conventional fluid reaction nozzles and supplement the reaction of the drive nozzle means. Control valve means permits the rotor to be removed whilst liquid flows in the system.

This application is a 371 of PCT/GB96/00125, filed Jan. 23, 1996.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to liquid cleaning systems of the type in which aliquid is pumped around the system by way of a self-cleaning, barrierfilter of the so-called back-flush type, and in particular relates tothe incorporation of a fluid-powered centrifugal cleaner to process thecontaminated liquid back-flushed from the barrier filter.

Self-cleaning barrier filter units are well known in the art in which ahousing contains a plurality of filter elements or discrete surfaceregions each having an inlet surface exposed to a common inlet chamberof the pumped fluid and an opposite, outlet, surface exposed to a commonoutlet chamber in which the filtrate, the cleaned fluid, is collectedbefore leaving the unit still under pressure. In addition, the inletchamber has a shield or cover member which is operable periodically toisolate each inlet surface in turn from the inlet chamber and connect itinstead to a rejection conduit which leaves the housing, so that as theshield member moves from element to element the temporarily shieldedelement is subject to reverse flow from the outlet chamber which servesto lift contaminant debris from the inlet surface of the element andflush it along the rejection conduit.

Such self cleaning barrier filter units may operate in a so-calledintermittent manner, in which the shield or cover member moves onlyoccasionally between inlet surface regions, and possibly limiting flowthrough the inlet surface region for a predetermined interval less thanthe total time it serves that region and/or whilst it is changingbetween inlet surface regions, or so that the flow of back-flushedliquid is more continuous but from a continuously varying, andfrequently cleaned, region of inlet surface.

Whereas it is conventional in full flow or barrier filter design thateach filter unit passes liquid with minimum pressure difference acrossit (subject of course to having a pore size to trap particles of therequired dimensions), it is found that to efficiently flush such trappedcontaminant particles from a filter requires a large pressure differenceto be available to establish a high flow rate through the filter andcarry them from the inlet surface region. However, if the filter elementshould become significantly or completely blocked to liquid passage,possibly over a period of time by inefficient flushing of thecontaminants, the prolonged and repeated application of significantpressure difference across the filter region risks effecting physicaldamage to the underlying structure of the pressure filter in thatregion.

Thus it is important to the operating life of the filter unit that theback-flushing removes contaminants from the back-flushed regionefficiently and without permitting a progressive accumulation.

Most simply the back-flushed liquid, despite the high concentration ofcontaminants, is returned directly to the reservoir from where it issubsequently pumped around the system and the solid contaminants areagain held by the barrier filter. Whereas such an arrangement ensuresthe contaminants are contained in the system between the reservoir andbarrier filter, the liquid in the reservoir does become progressivelymore contaminated.

As indicated above, a conventional full-flow or barrier type filterelement normally intends to produce a relatively small pressure dropacross it as liquid flows therethrough and it is known to interpose sucha further barrier filter between the back-flush arrangement and thereservoir to isolate solid contaminant without significantly reducingthe pressure difference applied across the back-flushed region of thefilter.

However, such further barrier filter whilst having of necessity asignificant surface area, is capable only of trapping a relatively smallvolume of contaminants and therefore is necessarily coarse if it is notto become blocked in a very short time. In practice therefore, suchfilters serves only to trap large particles whilst permitting smallparticles of soot etc to remain in the liquid. Notwithstanding theefficacy of such a further filter or dependence upon pore size, it isstill liable to require cleaning frequently to avoid introducing asignificant pressure difference to the back-flush arrangement; to avoidclosing down the system, which would negate any advantage from theback-flush arrangement in the barrier filter, it is considered apractical necessity to have at least two such further filters in aduplex arrangement so that one operates whilst the other is cleaned orreplaced.

An example of such a barrier type filter having back flush arrangementis disclosed in EP-A1-136202.

It will be appreciated therefore that such form of filtering ofback-flushed liquid involves capital and maintenance costs which may notbe justified for all systems, particularly in view of the limited rangeof solid contaminants removed thereby.

Within a liquid circulation system including such a barrier type filter,it is known to complement the filter, which traps contaminant particleson the basis of size alone and has limited capability to hold suchcontaminants, with a centrifugal cleaner in which contaminant particlesare separated on the basis of mass rather than size (although they arerelated for any particular substance) and which has the capacity to holda significant volume of separated contaminants.

Typically, within a centrifugal cleaner a substantiallyvertically-mounted, high speed rotor includes a contaminant-depositingcontainer, (more conveniently referred to simply as a contaminantcontainer) through which the fluid is passed and in which solidcontaminants are separated from the fluid to deposit on the containerwall from which they can be periodically removed or the containerreplaced. Such a centrifugal cleaner may have its rotor driven byexternal coupling to an engine or like rotary plant with which used,which results in a complex and expensive arrangement, or may, as is moreusual and considerably cheaper to implement, be driven by causing thefluid applied to the contaminant container under pressure to exit by wayof tangentially directed nozzle means, the reaction to which spins therotor at high speed essential for efficient centrifugal separation. Sucha fluid-cleaner, in which the rotor is driven by the fluid beingcleaned, is usually referred to as a self-powered centrifugal cleaner.

In such a self-powered centrifugal cleaner the liquid loses all energyin passing through the container, so that it has invariably been used ina by-pass mode, tapping liquid from a relatively high pressure part ofthe system in the vicinity of the full flow filter and returning itdirectly to the reservoir.

The use of such self-powered centrifugal cleaner in combination with abarrier type filter is disclosed in EP-A-0606578, the barrier typefilter delivering a constant supply of liquid, some of which may bediverted through the centrifugal cleaner to by-pass the rest of thecirculation system.

It is implicit in such self-powered centrifugal cleaners that reactionnozzle means must be dimensioned to create a significant pressuredifference thereacross to rotate the contaminant container at a speedhigh enough to affect centrifugal separation and also that the pressureand rate of supply of the liquid and be adequate to effect continuoushigh speed rotation or separation will not be efficient.

As an alternative to self-powered centrifugal cleaning, wherein all ofthe fluid is both subjected to centrifugal cleaning within thecontaminant chamber and creates rotation of the chamber by its ejectiontherefrom, it is known to split liquid supplied at uniformly highpressure into two streams, one to serving only to spin the contaminantchamber and the other to pass through for cleaning. Such arrangement isdescribed in U.S. Pat. No. 3,791,576 and U.S. Pat. No. 3,784,092 whicheach discloses a centrifugal cleaner in which a liquid stream pumpedfrom a reservoir at constant pressure is split so that part of it drivesthe centrifugal separation rotor and part of it entrains a dissimilarliquid, floating on the reservoir, into the separation rotor where thepumped and entrained liquids can be separated from the mixture alongwith any solid contaminants from the stream which are isolated andcontained.

However, in relation to back-flushing liquid from a barrier type filter,consideration of employing such an alternative cleaning mechanism to abarrier-type filter becomes unattractive not only because of thepotentially relatively low supply pressure and rate and consistency ofliquid supply, after passing through two lower type filter regions inseries, but more significantly because the pressure drop across thecontaminant container, whether able to rotate or not, significantlylimits that available across the barrier filter region for back-flushingto the extent that it may not clean completely and accumulation ofcontaminants occur. If complete blockage of the filter region were tooccur, such that there is in effect no pressure drop across thecentrifugal cleaner, when the filter region is subsequently exposed toback-flushing pressure, the aforementioned high and potentially damagingpressure difference across the region could occur.

Therefore cleaning back-flushed contaminated liquid by way ofconventially employed barrier-type or self-powered centrifugal cleaningdevices has not been perceived as an efficient cost effective activity.

It is an object of the present invention to provide a liquid cleaningsystem, including pump means and a barrier type filter having anintermittent back-flush arrangement, in which the heavily contaminatedback-flushed liquid is cleaned efficiently and simply by centrifugalcleaning.

According to a first aspect of the present invention, a liquid cleaningsystem comprises pump means, operable to cause liquid to flow throughthe system, a barrier type filter having a back-flush arrangementwhereby a proportion of the liquid after passage through the filterbarrier can be passed in a reverse direction through a region of saidbarrier, and a fluid-powered centrifugal cleaner including a rotorhaving a contaminant chamber through which the back-flushed liquid ispassed and rotor drive means responsive to consistently supplied fluid,separate from the back-flushed liquid, to effect rotation of the rotorabout a substantially vertical axis at at least a minimum speed requiredto effect centrifugal separation of solid contaminants from back-flushedliquid passing through the contaminant chamber.

An embodiment of the present invention will now be described by way ofexample with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of a liquid cleaning systemincluding pump means and barrier filter having an intermittentback-flush arrangement and in accordance with the present inventionincluding a fluid driven centrifugal cleaner for the back-flushedliquid, driven by system liquid provided by the pump means,

FIG. 2 is a sectional elevation through the fluid driven centrifugalcleaner of FIG. 1, and

FIG. 3(a) and 3(b) are cross sections through the base of the cleaner ofFIG. 1 taken in the direction A--A and illustrating operation of thecontrol valve thereof, in first and second positions which direct theback-flushed liquid through the cleaner or to by-pass it respectively.

DETAILED DESCRIPTION OF THE DRAWING

Referring to FIG. 1, a liquid cleaning system 10 comprises a reservoir11 of the liquid, pump means 12, a barrier or full-flow type filter 13,utilisation means 14 for the liquid, and a return 15 for utilised liquidto the reservoir.

The filter 13 is of a type having an intermittent back-flush arrangementsubstantially as outlined above, comprising a housing 16 containinginlet and outlet chambers 17 and 18 respectively and a plurality offilter elements 20 each comprising screens of metal mesh having what maybe termed an inlet surface 21, exposed to the inlet chamber 17, and anopposite or outlet surface 22 exposed to the outlet chamber 18. Thuspumped liquid enters the inlet chamber, passes through each filterelement from inlet surface to outlet surface and collects in the outletchamber before exiting to the utilisation means. The housing alsoincludes and intermittent back-flush arrangement 23 represented by ashield or cover 23' which is caused to move by an indexing mechanism(not shown) to close off each filter element 20, or its inlet surface21, in turn from the inlet chamber whilst leaving outlet surface 22exposed to the outlet chamber pressure. The shield 23 includes arejection conduit 24 by which liquid from the closed off element isremoved from the housing by liquid from the outlet chamber as pressurebeing flushed through the filter element in the reverse direction fromoutlet to inlet surface and, in doing so, entraining contaminantspreviously deposited on the inlet surface. It is known in the art thatit is desirable for the pressure difference across the filter elementduring back-flushing to be as large as possible.

Normally such heavily contaminated back-flushed liquid is returned tothe reservoir or further full-flow filter but in accordance with thepresent invention it is supplied to a fluid-powered centrifugal cleaner25 which forms part of the system and effects separation of solidcontaminants from the entraining liquid, permitting the latter to bereturned to the system by way of duct 26 and reservoir 11.

Referring now to FIG. 2, the centrifugal cleaner 25 comprises a housing,indicated generally at 27, having a base 28 defining a discharge region29 coupled to the reservoir 11 by way of passage 26 the latter being ofsuch cross-sectional area and slope as to facilitate drainage by gravitywhen the ambient pressure within the drainage region is normalatmospheric pressure. The base supports spindle means 30 extending fromthe base along an operably vertical axis 31 through the housing, thespindle means supporting at its other end a relatively thin cover 32which extends axially to abut the base at joint 33 and is removable fromthe base.

The spindle means contains a main inlet passage 34 extending part waytherealong connected, by way of inlet duct 35 (FIG. 3(a)) in the base,to rejection conduit 24 to receive back-flushed liquid.

The housing further includes a rotor 40, supported on the spindle meansfor rotation thereabout, comprising an annular contaminant chamber 41apertured and in communication with the discharge region 29 by way of alower part 42_(L) of a stand tube 42 apertured at 43, and nozzle means44 comprising a plurality of substantially tangentially directed nozzles(also indicated as 44) arrayed about the axis 31. The stand tube 42comprises a radially inner wall of the contaminant container 41 and anupper part 42_(U) of the tube separated from the base part by septum 45is apertured at 46 and in communication, in a manner to be describedmore fully hereafter, with the main inlet passage 34 by way of a mainrotatable fluid coupling shown generally at 47.

The centrifugal cleaner as thus far described is conventional exceptinsofar as the nozzle 44 may be dimensioned to offer a relatively smallpressure drop for liquid passing therethrough, as opposed to arelatively large pressure drop conventionally required to effect highspeed rotation of the rotor by reaction to liquid ejection from thenozzles. The nozzle dimensions may create some pressure drop in theejected liquid that exerts force on the rotor by reaction to liquidejection, although it may not be sufficient on its own and in responseto the inconsistent supply of liquid to effect high speed rotation, andin that sense the nozzle means (and nozzles) 44 may be referred to asliquid reaction nozzle means and nozzles respectively.

In accordance with the invention the centrifugal cleaner also includesfluid operated drive means, indicated generally at 50. This drive meanscomprises a first part fixed with respect to the housing, in the form ofan auxiliary inlet passage 51 associated with the spindle means andextending at least part way along the spindle means and through the baseand connected to receive a supply conduit 52 to receive drive fluid atsuper-ambient pressure, (the ambient pressure of the discharge regionbeing considered as ambient), being system liquid from the pump means12. The drive means also comprises a second part comprising fluidreaction nozzle drive means 53 comprising a plurality of substantiallytangentially directed drive nozzles (also indicated as 53) carried bythe rotor and opening to the discharge region 29, a plurality of driveconduits 54 individually connecting the drive nozzles 53 to theauxiliary inlet passage 51 by way of an auxiliary rotatable fluidcoupling 55. The drive nozzles 53 are conveniently contained in a lowerwall of the contaminant container adjacent the liquid reaction nozzles44, the associated drive conduits extending through the contaminantchamber thereto.

The fluid drive means thus receives a consistent, and convenientlyconstant, supply of relatively uncontaminated liquid from the pump meansat a rate and pressure regulated by the pump means and/or the dimensionsof any of conduit 52, inlet passage 51, conduit means 54 or drive nozzlemeans 53, and is response to ejection of the pumped liquid by way of thedrive nozzle means 53 to rotate the rotor at at least the minimum speedto effect centrifugal separation of solid containments from theback-flushed liquid passing through the contaminant container 41. Theback-flushed liquid, insofar as it periodically has a super-ambientpressure, may react against the nozzle means 44 on ejection therefore tosupplement the reaction on the rotor from drive nozzle means 53 andprovide supplementary reaction nozzle means which serves to increase therotation rate and thus efficiency of contaminant separation.

Although a proportion of the pumped liquid is used by the drive meansafter which it is returned from the discharge means to the reservoir (orfurther cleaning operation) with the centrifugally cleaned, back-flushedliquid, the drive nozzle means is dimensioned such that only arelatively small proportion of the pumped liquid used as the drive fluidis prevented from reaching the utilisation means 14 and readilycompensated for, if necessary, by slightly increasing the outputpressure and/or delivery rate of the pumping means.

It will be appreciated that the conceptually simple provision of thefluid drive means may be implemented in the centrifugal cleaner in manyways, of which that shown in FIG. 2 is only one, but the manner in whichthe drive fluid (pumped liquid) is supplied from the stationaryauxiliary inlet passage 51 to the rotating conduit means 54 in additionto the supplying back-flushed liquid to the contaminant container is ofpracticable significance.

Considering the spindle means 30 more closely, it comprises, staticspindle 60. The rotor 40 includes a bearing tube 61 journalled to thespindle at 62 and 63 towards each end thereof and defining between thejournals an annular tube space 64. The spindle has formed therein saidmain and auxiliary inlet passages which communicate with the annulartube space by way of main and auxiliary radial aperture means 65 and 66respectively separated from each other in the axial direction. Eachaperture means may comprise one or more apertures arrayed around thespindle. Tube seal means 67 extends between the bearing tube and thespindle at an axial position between the main and auxiliary radialaperture means to separate the tube space into discrete main (upper) andauxiliary (lower) regions respectively. The bearing tube is apertured inthe main region at 68 to communicate with the contaminant chamber 41, byway of stand tube upper region 42_(U) and aperture 46, and is aperturedin the auxiliary region at 69 to communicate with individual driveconduits 54, thereby providing said main and auxiliary rotatable fluidcouplings 47 and 55 respectively.

The main and auxiliary inlet passages conveniently are formed in a blindrecess 70, extending from the end of the spindle supported on the base28, in which the passages are defined coaxially one within the other.

The recess extends at least as far as the main radial aperture means 65furthest from the base and contains a pipe 71 of smaller cross-sectionalarea which extends axially to a position between the main and auxiliaryradial aperture means at which it is sealed at 72 to the spindle todefine the main inlet passage within the pipe and recess (communicatingwith the radial aperture means 65) and the auxiliary inlet passagesurrounding the pipe (communicating with the other radial aperture means66).

It will be appreciated that by adopting such a structure for the (hollowtube or drilled) spindle means, a spindle within a conventionallyjournalled bearing tube that provides a contaminated liquid inlet forthe rotor of a conventional self-powered centrifugal cleaner may bereadily adapted to provide an auxiliary inlet passage whilst avoidingany orientation problems in aligning the passage within the spindle withcontinuations thereof in the base, permitting the spindle to be simplysecured to the base by a screw thread 73.

It will be appreciated that a principal reason for employing such abarrier filter having a back-flush capability is to operate the systemfor a prolonged interval without the necessity to stop it for removingcontaminants from the surfaces of the filter element screens. Inaccordance with the present invention the centrifugal cleaner hasassociated therewith control valve means which is operable to facilitateremoval of the rotor with its contaminant container during continuedoperation of the system and barrier filter, that is, contemporaneouslywith the supply of liquid and drive fluid to the centrifugal cleaner.

The housing 27 contains within the base 28 thereof control valve means80 comprising a drive fluid part 81, operable to pass or impede thepassage of drive fluid to the auxiliary input passage 51 and a`back-flushed liquid` part 82, operable in conjunction with the part 81to divert the flow of back-flushed fluid received in duct 35 from themain inlet passage 34 to the discharge region 29 by way of passage 26leading from discharge passage 83.

The parts 81 and 82 of the control valve means are defined by a singlevalve body 84 extending through an aperture 85 in the housing base towhich supply conduit 52 is coupled. One end 86 of the valve bodyprotrudes from the aperture, permitting it to be rotated about itslongitudinal axis, whereas the other end 87 extends to a part of theaperture which comprises an extension of the aforementioned supplyconduit 52 for receipt of drive fluid and beyond the junction of theaperture with inlets passage 51.

The valve body end 86 has a recess 88 extending axially from the end toreceive drive fluid from supply conduit 36 and a lateral aperture 89 topass it to inlet passage 51 or block its passage, depending upon theorientation of the valve body about its axis, defining thereby a drivefluid part of the control valve means. The valve body also includes acut-off valve 90 comprising a piston 91 extending along the recess andbiased by spring 92 towards the recess end 86 to isolate the lateralaperture 89 from received drive fluid irrespective of the orientation ofthe valve body. The cut-off valve is responsive to drive fluid pressurein excess of the predetermined minimum acting thereon to be displacedagainst the bias to permit the drive fluid to exit lateral aperture 89to the auxiliary input passage, that is, the centrifugal cleaner onlytakes drive fluid from the system when pump delivery pressure issufficient to sustain its loss.

Referring also to FIGS. 3(a) and 3(b) the valve body 84 also has agroove 95 extending part way about its periphery that defines a recessbetween the body and the aperture wall such that in a first rotationalposition of the valve body, wherein the lateral aperture 89 is alignedwith inlet passage 51, the groove 95 is disposed to connect back-flushedliquid receiving ducts 35 and main inlet passage 34 whilst blockingdrain passage 83. When the valve body is rotated to close the ducts 34and 35 from each other, isolating the auxiliary inlet passage from thedrive fluid, the groove 95 directs back-flushed liquid to the dischargeregion by way of drain passage 86 and isolates the main inlet passage,thereby permitting the housing to be opened and the rotor 41 to beremoved without stopping liquid flow through the system. It will beappreciated that whilst the centrifugal cleaner is isolated, any heavilycontaminated back-flushed liquid is discharged directly to thedischarged region and may find itself returned to the reservoir.Although such contaminants will eventually be trapped by the barrierfilter and removed by the centrifugal cleaner when it is subsequentlyoperating, even such occasionally presented contaminants, and theback-flushed liquid bearing them, may be eliminated from the system bythe discharge duct 83 discharging outside of the system, to waste,rather than the drainage region 26 which feeds to the reservoir.

It will be appreciated that numerous variations may be made in respectof the structural details of the above described fluid-poweredcentrifugal cleaner without departing from the scope of the invention.

For example, the control valve means may take different form such as aspool valve, be disposed separately from the housing or be omittedaltogether.

The first and second parts of the drive means may also take the formother than described above in detail. For example, the first part maycomprise an auxiliary inlet passage other than extending coaxiallysurrounding the main inlet passage defined by a central recess in astatic spindle.

A unitary static spindle extending from the base and/or housing coveropposite thereto may have main and auxiliary inlet passages extendingside by side from the same end, or from opposite ends, or may be a pairof stub spindles extending one each from the base and housing cover.Although it is convenient to define the auxiliary passage within aspindle, it may additionally be defined within the base and an annularpassage space surrounding the spindle that comprises rotatable couplingmeans of the second part. Depending upon how the inlet passages aredefined, the main radial aperture means may be the lower, rather thanupper, aperture if liquid is to enter the contaminant container towardsthe lower end thereof, possibly if the exit is by way of reactionnozzles at the upper end of the rotor.

The second part of the drive means may therefore have conduit means 54receiving drive fluid from the spindle means at any axial position andextend to drive nozzle means at any axial and radial position withrespect to the rotor. Such drive nozzle means need not comprise avertically disposed arrangement in a section of the base of the rotor,that is, extending through the wall of the contaminant container from aconduit within, but may comprise a simple nozzle defining the end ofdrive conduit means that extends outside of the contaminant container.

The fluid reaction drive nozzle means need not be fixed with respect tothe rotor, provided it is coupled in respect of rotation about the axisto cause the rotor to rotate with it.

As an alternative to supplying fluid to drive nozzle means outside ofthe contaminant container by way of conduit means and a rotatablecoupling means which defines an annular chamber surrounding the axis,such an annular chamber may extend radially, to a distance from the axisat which the reaction nozzle means may be defined in the walls thereof,for efficient rotation of the rotor contaminant container coupledthereto; that is, the rotatable coupling means may comprise a containerfor the fluid similar to the contaminant container and disposed in linewith, or possibly inside of, the latter.

Notwithstanding the structure of the drive reaction nozzles 53 they neednot be disposed at the same rotational positions as nozzles (44) for thecleaned back-flushed liquid, nor in vertical alignment therewith,provided the tangential direction which produces rotation is maintained.

The drive means, as described hereinbefore functions by ejecting fluidfrom nozzles means which is free to rotate about the axis as a reactionto ejecting the fluid. It will be appreciated that in an alternativeform the rotor may be associated with, and coupled thereto for rotation,a set of impeller blades which are disposed within the discharge regionto receive drive fluid from static nozzle means arranged to eject thefluid from the base or housing cover to impinge directly on them andgenerate a rotation force.

Notwithstanding the mechanism by which the fluid drives the rotor andits contaminant container at high speed, the back-flushed liquid whichis passed through the contaminant chamber may exit the chamber and therotor by other than the reaction nozzle means of the type conventionallyused for centrifugally cleaned fluid to self-power the rotation, as thedrive fluid provides sufficient reaction to maintain rotor speed; theliquid may for instance exit via slots or large diameter holes anywherein the base of the rotor, possibly in line with the lower end of thestand tube 42 or where the reaction nozzle means 44 would normally besited. Such nozzles, or their alternatives, may be dimensioned toprovide a maximum pressure difference thereacross so that maximumpressure difference is available across the back-flushed filter regionfor optimum flushing of contaminants therefrom.

It will also be appreciated that whereas it is convenient for the drivefluid to comprise the liquid pumped through the system, and thusmiscible with the cleaned liquid in the discharge region 29, it maycomprise a fluid, liquid or gas, from a separate source.

The supply of fluid is required to be consistent to maintain therotation momentum of the rotor such that any back-flushed liquid itreceives is subjected to centrifugal separation of contaminants. To thisend the supply of fluid need not be constant, but could vary in supplyrate or pressure cyclically, possibly, pulse, such that it effects andmaintains rotation of the rotor above a predetermined minimum speed toeffect centrifugal cleaning.

If it is necessary to maintain segregation between the drive fluid andthe back-flushed liquid, individual, radially separated, annulardrainage regions may be defined in the base of the housing and the baseof the rotor for the fluid and liquid and the reaction nozzle meansarranged such that the cleaned, back-flushed liquid and the drive fluidexits into the different discharge regions.

Alternatively, a drive fluid immiscible with the back-flushed liquid maybe discharged into a common discharge region but separated therefromlater, possibly by a further centrifugal device which separates fluidson the basis of their densities. The ambient pressure defined by thedrainage region may be other than atmospheric pressure providedappropriate steps are taken to facilitate drainage.

Despite the numerous structural forms that such a separately fluidpowered centrifugal cleaner may take, it will be seen from the specificembodiment described in detail that it is capable of being readilyimplemented by adaptation of a form of centrifugal cleaner self-poweredby the liquid being cleaned, by adapting the reaction nozzles means,liquid inlet passage means along the spindle means to accommodate anauxiliary inlet passage, bearing tube to provide auxiliary rotatablefluid coupling into drive conduit means and additional reaction nozzlemeans to form the drive nozzle means, and furthermore by driving therotor by reaction to the liquid of the system from which theback-flushed liquid is received.

The above description has been based on the back-flush arrangement beingof the intermittent type, receiving liquid from discrete barrier filterelements with a reduction in flow at least during transition of theshield 23'. It will be appreciated that the back-flush arrangement mayhave a comparable shield or cover continuously and frequently exposing avarying, relatively small, region of an inlet surface not divided intodiscrete elements to such reverse flow of liquid from the outletchamber.

I claim:
 1. A liquid cleaning system comprising pump means operable tocause liquid to flow through the system, a barrier filter having aback-flush arrangement whereby a proportion of the liquid after passagethrough the barrier filter is passed in a reverse direction through aregion of said barrier filter to create a back-flushed liquid: afluid-powered centrifugal cleaner including a rotor having a contaminantchamber through which the back-flushed liquid is passed; and rotor drivemeans responsive to a supplied fluid, separate from the back-flushedliquid for effecting rotation of the rotor about a substantiallyvertical axis at at least a minimum speed required to effect centrifugalseparation of solid contaminants from the back-flushed liquid passingthrough the contaminant chamber.
 2. A liquid cleaning system as claimedin claim 1 in which the rotor drive means is arranged to receive andrespond to drive fluid comprising pumped liquid of the system.
 3. Aliquid cleaning system comprising pump means operable to cause liquid toflow through the system, a barrier filter having a back-flusharrangement whereby a proportion of the liquid after passage through thebarrier filter is passed in a reverse direction through a region of saidbarrier filter to create a back-flushed liquid; a fluid-poweredcentrifugal cleaner including a rotor having a contaminant chamberthrough which the back-flushed liquid is passed; and rotor drive meansresponsive to a supplied fluid, separate from the back-flushed liquidfor effecting rotation of the rotor about a substantially vertical axisat at least a minimum speed required to effect centrifugal separation ofsolid contaminants from the back-flushed liquid passing through thecontaminant chamber; and wherein the fluid-powered centrifugal cleanercomprises a housing havinga base, defining a discharge region at ambientpressure, and spindle means, comprisinga static spindle extending alongan operably vertical axis through the housing, a bearing tube, carryingthe rotor affixed thereto, journalled to the spindle and definingbetween axially spaced journals an annular tube space apertured tocommunicate with the contaminant chamber, and an axially extending maininlet passage formed in the spindle communicating with the annular tubespace by way of main radial aperture means and arranged to receive saidback-flushed liquid, and further whereinsaid fluid powered rotor drivemeans comprisesa first part comprising an auxiliary inlet passage,extending along the spindle to receive therein said drive fluid separatefrom the back-flushed liquid, and auxiliary radial aperture means,spaced axially from the main radial aperture means, communicating withsaid bearing tube space, and a second part comprising rotor seal means,extending between the bearing tube and spindle at an axial positionbetween the main and auxiliary radial aperture means to separate thetube space into discrete main and auxiliary regions, and a plurality oftangentially directed fluid reaction nozzles, and a plurality of driveconduits individually connecting said drive nozzles to the auxiliaryregion of the tube space to direct said drive fluid from the auxiliaryinlet passage to the reaction nozzles.
 4. A liquid cleaning system asclaimed in claim 3 in which each drive nozzle is defined in a wall ofthe contaminant chamber.
 5. A liquid cleaning system as claimed in claim4 in which the rotor drive means comprises also at least onetangentially directed supplementary fluid reaction nozzle operable topass back-flushed liquid from the contaminant chamber to the dischargeregion to produce a rotational force on the rotor related to liquidpressure within the container supplementing the force produced by thedrive fluid, and wherein each said supplementary reaction nozzle isdisposed adjacent a drive nozzle in said wall of the contaminantchamber.
 6. A liquid cleaning system as claimed in claim 3 in which thefluid-driven centrifugal cleaner includes control valve means, operableto permit removal of the rotor contemporaneously with supply ofback-flush liquid to the cleaner from the barrier filter.
 7. A liquidcleaning system as claimed in claim 6 in which the control valve meanscomprises a drive fluid part, operable to impede or pass drive fluid tothe first part of the rotor drive means, and a back-flushed liquid partoperable, in conjunction with the drive fluid part impeding the flow ofdrive fluid, to divert the flow of back-flushed liquid from the maininlet passage to the discharge region.
 8. A liquid cleaning system asclaimed in claim 3 in which the fluid-driven centrifugal cleanerincludes control valve means, operable to permit removal of the rotorcontemporaneously with supply of back-flush liquid to the cleaner fromthe barrier filter, comprising a drive fluid part, operable to impede orpass drive fluid to the first part of the rotor drive means, and aback-flushed liquid part operable, in conjunction with the drive fluidpart impeding the flow of drive fluid, to divert the flow ofback-flushed liquid from the main inlet passage to the discharge regionand the drive fluid part and back-flushed liquid part are defined by asingle valve body extending through an aperture in the housing, to whichaperture said drive fluid is supplied at one end of the valve body to bediverted laterally thereof to said first part of the rotor drive meansor blocked by the valve body in dependence upon the position of the bodyin the aperture; and wherein said main inlet passage, discharge regionand a back-flushed liquid duct are in communication with a differentpart of the valve body having a recess between it and the aperture,which recess is operable to connect either the main inlet passage or thedischarge region with the back-flushed liquid duct in dependence uponthe said position of the body in the aperture.
 9. A liquid cleaningsystem as claimed in claim 8 in which the control valve means includes acut-off valve comprising a piston, extending along a recess in the valvebody and biased towards said one end of the valve body, responsive todrive fluid pressure below a predetermined minimal level to close thefirst part of the rotor drive means from the drive fluid source andresponsive to drive fluid pressure in excess of said minimal levelacting thereon at the end of the valve body to be displaced against thebias to admit the drive fluid to said first part of the rotor drivemeans.